The present invention relates to a microwave level gauge adapter having a thermal barrier for use with a tank level sensor.
Level gauges are generally used in the process control industry to measure the level of material contained in a tank. As used herein, the term “tank” refers to a container, receptacle, vessel or other device for holding gases, liquids or solids. Radar level gauges are often used to measure process fluids or process solid levels in tanks, where the process materials range from benign materials to severely corrosive or abrasive compounds.
One type of level gauge for measuring a level of material in a tank is called a microwave level gauge. Microwaves are high frequency, short wavelength, electromagnetic waves. Microwaves, because of their short wavelengths, tend to travel in straight lines. This property gives rise to their application in radar, where objects are detected by the reflection of microwaves.
Generally, microwave or radar level gauges transmit an electromagnetic pulse into the materials contained within the tank, and measure the level of the process materials using the reflected pulse. As used herein, the term “microwave” refers to a high-frequency electromagnetic wave. The term “microwave pulse” refers to a microwave signal of short duration that is transmitted on a microwave antenna or conductor. The terms “microwave antenna” and “microwave conductor”, as used herein, refer to a conductive structure specifically designed to couple high-frequency electromagnetic energy (or to radiate electromagnetic energy). Typically, the microwave antenna or microwave conductor can both transmit and receive electromagnetic energy.
In a conduction waveguide assembly, the antenna typically extends from a transmitter assembly into the process materials. For example, a microwave pulse travels along the antenna, and is reflected back when the pulse encounters a material with a different dielectric constant. Generally, the pulse is affected by the change in the dielectric constant at the surface of the process material within the tank. Various techniques may be used to analyze the reflected microwave pulse (including, for example, time domain reflectometry).
Since the process materials within the tank tend to be corrosive and are often stored under pressure, there is a process seal positioned between the sensor and the potentially aggressive materials within the tank. Conventionally, an O-ring or a teflon seal was used to isolate the process fluid from the transmitter housing and sensor electronics. In addition to isolating the electronics from the process fluid, such seals were typically constructed of materials selected so as not to cause microwave reflection.
While such seals typically met microwave transmission requirements, the seals were not particularly well-suited for high pressure/temperature applications.